Method of cutting gears



g- 1933- E. WILDHABER METHOD OF CUTTING GEARS Filed March 19, 1928 3 Sheets-Sheet l g- 29, 1933- E WILIDHABER; 1,924,476

METHOD OF CUTTING GEARS Filed March 19. 1928 5 SheetJs-Sheet 2 Fl G. 12 Fl G15 31 I 82 INVENTOR E/mv W'VuAA/M Aug. 29, 1933. E. WILDHABER METHOD OF CUTTING GEARS 3 Sheets-Sheet 3 Filed March 19, 1928 FIG-18 INVENTOR generated from ,the" tooth shape of said. rack Patented Au jze, 1933' a a 2M mmnq ior s nrise "Gms 1 Ernest Wildhaber, Brooklyn, N-.'Y.1

Application March 19,1 192's.) se m... 262,376

. I13] (aims.

-' The-present invention relates tomethodsoi':

cutting gears, and particularly to such methodsin which a tool is rotated in engagement with a con-- tinuously .rotating. gear blank. Tools of this T character are ordinarily known as hobs.

through its meshwith the gear blank, as ,well known.

' 5 0ne objector-the present invention is to provide with known hobbing methods otthe character re 1 ;-giving a smoother cutting operation and a method consuming less energy or power. a

-a hobbing method producing a superior finish on thet'ooth suriaces of a gear blank, as compared ferred to.

i Another aimis toprovide a hobbing method to effect; anincreased A still further objectis output ofg'ears. M a Another object isto provide a method for cute i ting helicaland herringbone gears witha reduced feeding distance..-

Other objects will be apparent in; ile coiirseof V the specification and from recital oi the appended a My invention is ,illustrate d by .way of examples in the accompa'nyingdrawings, in which: Figjil is a partial section of a hob, the section,

, being taken'substantiallyfin the direction of,the l hob axis, and apartial view of a gear blank shown -in engagement' withsaidl'hob. M Fig. 1 am singtive of an embodimentfoi my invention preferably applied to gears with large numbers of teeth. J q j 1 of my inventionpreferablyappliedto glearjslwith i Fig. i 2' is a partial section of anotherhob, shown in engagement with a gear blank,-of which'only :a

ortion isfshown. Fig. 2 illustrates a modified I embodiment of my invention. a i I v Figl 3 is 'a partial section of a further hob,.and .1 a partial view of 'a gearblank'in engagmentwithj said'h'ob. Fig. 3 is illustrative of anenibodiment moderate numbersoi teeth.. H

Fig.4 is an end view of the hob shown inFig. 1, partly a section taken at right angles to the axis- .otthe hob.

" -,5 e V ew Pa t i s e e'h circumference of-a hob of the ment with a hob;

[both Fig. 1 and Fig. 17,,

the generaltypeindicatedin theFigures Fig.v 6 and Fig; rare developments at ajreduced scale oi hobsof the general type indicated-inthe of flutes. The periphery 6 (Fig.4) vhas beende veloped into a plane;

Figures '1 and 4, illustrativeof two arrangements I p 7.

Fig. 8 is a development at a reduced scale of the;

tratedinfthe Figures ;2;and 3.

. Fig'. 9 is a development of a roughinghob -fl Fig. 10 isa partial section of a hob, said'sece,

general type ill-115:

tion being taken substantially in the direction of the hob axis, and a-partialview of a gear.

blank in engagement withsaidhob. Fig. 10 illus tratesan embodiment of my invention preferably applied to gearswith small numbers of teeth.

.Fig. 11 is an end view oi the; hob shown in.

i "12 and Fig. 13are sections through-racks; of increased profile inclinationorincreased pressure angle, such' asmayv "alsojbe, represented or.

embodied with hobs inaccordance withthe pres-= ent invention. It is noted that the profiles ofthe racks are curved, and that the racks'there s0 n engage- 1 i fore correspondto noninvolutefgears. :Fig. 14 is a'planiv iewof a gearblank .Fig. 15 is afront elevational viewcorrespond I ing to Fig.; 14 and-indicating "in addition the chief partsoi asimplifieddevice for generating. gears. a v va -ii; 1 The Figures 161to -20 illustrate'aj preferred. embodiment of {the present invention as to helical and herringbone gears. l 1-6 and Fig. l'l areplan-views ofa helical applied V gear. and; of a hob in engagement. therewith,

illustrativeof' twodifierent settings ofthe hob,

the preferred. setting being illustratedin'Fig. 16.=

;Fig. 18 is anormal section through the teeth of a .helical gear a long lines 8-.8 of Fig-16- and' Figal'l, and a section throughthethread of a hob engaging withsaid teeth. lzjart ofsa'id" f n I I 7 Figures 19 and .20 are ,plane sections'through the threads of the hobsindica'ted in theFigures: lfiand 17 respectively, and through racks which are Gonjugate to said threadsfl i 1 In Fig.1 andFig. 4,.the numeral-11 denotes;-

a hob. having a,plurality of-cutting..teethf 12,

u with cutting edges such as which are provided 13.14., V V 1 15.1. In the case illustrated in Fig'.- 1,, said rack? gear is shownin' view. ,Fig. 18-corresponds to.

Ho 1 orrepresents a rack" its position and motion relatively to gearzbla'nk; 1L0.

contains straight or approximately straight profiles, characteristic to the involute system of gears.

15 while rolling on the pitch circle 16 of the 7 gear blank. That isto say said rack meshes with the gear blank exactly in the same way as a mate gear meshes with said gear blank. [The two lines of-action which correspond to the two sides of the teeth intersect then in a point that isto say the angle included between the cutting face and the plane. tangent to theunrelieved athreadof the hob. t v In Fig. 7, the cuttingteeth32 of thehob are 17' of the pitchcircle, as well known.

The rack embodied by hob 11 has a different and smaller pressure angle, than the pressure angle at which the gear blank meshes with a mate gear. The said rackmeshes' with gear blank 15 in suchmanner, that a line .18ofthe rack rolls ona circle 20 of the gear blank. The

two lines of action 22, '23 between :said rack and the blank intersect then in point 21 of circle 20, namely in the point at which the rolling-con tact takes place,"that'is to" say at the instantaneous axis of relative motion,as is'known.

It is also known, that exactly the same tooth profiles 24, 25 may be formed on the gear blank by arack having a pressure angle different from the" pressure angle of the gear blank, and-by a rackhaving a pressureangle equal to the pressure angle of the gear blank, as long as the perpendicular'piteh 26 (Fig. 1) is the sameon the two racks.

By providing ahob as indicated in Fig. 1,

the'lines of action 22,23 between rack and gear blank have been separated in the zone of the Inasmuch {as the finishing cuts are a teeth. plied to the gear blank 15 alongthese lines 22 23, thefinish-cutting edges 13' which finish along line 22 form a group separate from the group.

constituted by the finish cuttingedgesv 14, which In accordance with the present invention different cutting faces are provided adjacent the cuttinge'dges ISMa'ndadacent the cutting edges 14. r The cutting faces adjacent the cutting edges 13 are formed by flutes. or'gashes of such inclination as'to formkeen cutting'edges 13. "And the cutting faces adjacent cutting-edges .14 are so inclined as to'furnish keen cutting edges 14.

ln'other words thecutting faces'contain'a'rake,

."in such manner thatlthe cutting angle is smaller than 90 in any point of a cutting edge 13, and of a cutting edge-14 respectively. r

Preferably helical cutting "faces; of different inclination are provided. Reference is made to the developmentsFig. 6 andFigJl, which relate to a hob containing a'single thread and to a} hob containing multiple threads'respectively. I i In Fig. fi'relieved cutting teeth 28 are arranged in the form of a single thread, and flutes 30, 31 .of different inclination are-provided, 'to' forzn' keen finish cutting edgeslS and 14 respectively.

The cutting faces arefor'med on the sides indi catedin heavy lines, that is to sayon the sides facing towards'the ends of the" hob. Preferably V the flutes 30, 31' are equal in number, and moreover are preferably'made helical,- that is to "say- 7 helices on the surface of the hob, and are indicated by straight "lines in (levelthey extend along opment; It is seen that the two systems offiutes .30, 3l-"consti'tut e'what might be termed herringe They areof oppositehand, andit is noted that the flutes 31 are of a hand equal to the: hand of the hob-thread, nam'elyof right hand in theexample illustrated; The flutes are seen toreach into or even over eachother. For con a or the other.

direction of .relative motion of the cutting edge,

arranged in the form of multiple threads and in When the lead consequence furnish a larger inclination of the fith'read, or a largerlead angle. 7 angle is large enough, straight flutes 33 extending in the direction of the hob axis'may' be provided insteadof thehelicalfflutes 3'1 offFig.'6,',to effect keen cutting-'edges-l l; Helical flutesBl are: disposed sofas to effect 'keen -cutting' edges 13', 7

that is to say to effect aside rake adjacent said cutting edges. I The'flutes 34 are seen 'tobe arranged also somewhat in the-m'atterof herringbones.

To resharpen'the cuttingedges, the -flutes are.

reground, as well known. Small grinding wheels are required especially in the case illustrated 'in Fig. 6, according to which every cutting tooth is utilized'and provided'with a rake eitherone way i 35, 36 are not provided with keen cutting edges.

In the embodiment indicated Fig. '7 some of thecutting teeth, such as-teeth The edges of these teethj stand back from the uni'elieved thread, and do no cutting work; Such teeth could be removed, if so desired;

When renouncing thecutting action offsome of the cent-r'allylocated euttingteethf 35,361 the flutes (33, M'Ymay be regrourid' with a larger: grinding wheel. This appliestd hobs with single threads as well as to hobs with multiplethreads, and is preferablypracticed in: either case.

7 The profileof thecutting' faces,'a plane at right angles to the'aXis ofthehob, maybe made radial in analogy with the conventional shape of flutes are provided such as for instance indicated the tops :40 ofthe "cutting teeth.

otion especially of helical flutes. Preferably .liowever nonradial" in Fig. 4, where 33 denotes anonradial'profile, 1

In Fig; 5 anothertypefof nonradial p1'ofile 41 Hobs having flutes ofthis character can" be ground'on therelieved. sides-4 2 of their: teeth isillustrated." Flutes oft his character may be provided on finishing hobsgin which the tops '40 somewhateasierwiththe knownmeth'ods of re-- lief grinding, becausethe grinding line'or line of,

grinding contact (43in Fig; 5)" is more in the direction of the'cutt'ing edge 44. When afront rake is provided the grinding line would still be substantially like 43, "whereas a cutting edge A coincidence of cutting-edge and grinding line would have a direction 45, at an angle to line 4 3;

. .145- is found to bean advantage in practice, on account of reduced interference between the grind 7 ing wheel and a cutting tooth adjacent toth'e one which is'in grinding contact. q In the embodiments indicated in Fig. 12 and Fig. Brin finish cutting edges50, 51 are facing V; V V g 1,924,476 the outsideends ofthe hobs, Y The finishingcuts are iapplied along lines of 'action"'52 ,53 o'f'increased pressure angle, as comparedwith the" pressure angle of the gear blank} whereas'accorde ing to Fig. 1 the lines of action 22,2 3fcorrespond to reduced pressure angles. The embodied through the hobs in accordance with Fig. 2 and with Fig. 3 mesh with the gear blanks inla man her that themes 54 of t he racks rollon the cit cles"55;"whieh"are difierent from the'pitc ir-I cles" 16.

EmbodimentFig. ;2 and embodiment Fig; 3 dit-i c fer from each other somewhat in the outsideshape of thehob's. According toFig; 2 the'foutsideof the hob follows the tooth bottoms" 56' of =the'b1ank 57-0 Iii-Fig. "?the' 'outside surfacemf the hob is also curvedlengthwise, but the radiusfof curvature is larger than the-root radius ofthe -gear"- blank. The outside surface of thejhob may also] be made cylindricalI Generally the outside sur direction a I q While according to FigL'B' asinglelhob lS'PI'O" blank. In this "c asethe two sides 50, 580i the 'f-thetwczp sides of the teethiwere arranged in, sep- 2 forfinishingthe two'sides of the teeth of a gear hob threadare preferably made "of different in-' clination with respect to the hob axis 60;;

'"ln correspondence with the difierent'position of the finish cuttingcdges, hobs 'o'ff'th'e type illu's 'trated'inthe' Figures 2}3 and 5' are provided with cutting faces 61', 62 (Fig; 8) which face towards hereliefoi the hob teeth may 1y, an'd equal to the ordinarily used known relief.

the center of the hob, to effect keen cuttingedges This relief issometimes known as radial relief," -Howe v er side r'eliefor 'axial'relief may-"false be; used, in" short any known typeof relief may-be: ppneem the hobs operating in accordanceiwith the:presentinventions I i In the embodiments oflthe present j invention am gr ups; and'disposed on different cutting teeth. A cut'tingtooth thehcohtainS only one finish cutting edge, 'and it is' therefore possible to proyide on's'aid' cutting tooth a euttingface, which suits said: finish cutting edge and eflects a keen finish cuttingedge. The principle of 'sepn arating" the'finish cutting edges and providing" suitablecutting faces on the respective cutting teeth is not confinedto hobs but can be applied more broadly, for instance also to planing tools of-s rack shape. The rack section of Fig, 1 can namely be considered as part o'fa rack'shapedplariing Hitherto-it roughing hobs. V Imagining" that in Fig. 1 the di-' rections of rotation'aresuch, that-the s'ide'64 of the rack [section is rolledgintdtheblank andthe" other side .65 is correspondingly rolled out of en-i gagement' with the blank; then it is seen that for be made inward so far describedfthe jcutting edges for finishing" ad been a question of finishing hobs I; only. "Inasmuch as the roughing actiondiffers' substantially from the'fin'ishingaction of hobs, f a word'will now also be said about roughing and;

"straight; but will stock froni the tooth-space6ti in the roughingaopgearblankwhich had been well roughed out, edge 3 66; ill simply move in'toa spacepreviouslycutT i 'out anddono cutting. Q!

withreference also the Figures 1 to 8,"*the cuttingfaceismadeitoifavorli the finish cutting edges (13, Fi g'.f1):-so rnuchg-that the cutting-angle onthe opposite edges is-jsornez-r *In the hobs' de'scribed therefore not asgood-a cuttingactionasisdesir able :to remove theconsiderable amoufnt of stocks Q during roughing.

"'A jc'onsideration'ofFigk lrevealsithat the 'iin-" :is'h cuttingtedges 13 confine 'their action toc fin-l ishing only and that'they doinot remove much-z stock. In the roughing operation; where thebullci of the material is removed by -.'the edges 66 and t 67, fit is therefore unimportant whether or nota the edges 13 are very keen, aslon'g'as the edges 66 5 I and 67are keen and provide agood'cuttingaction, 4

For this'rea'sonli do. not i provide: the describedIv herringbone typeof fflutes on hobs accordingftoy I I Fig. 1' and Fig.4," when such hobs shallserve for? roughing only. 'Aisingle system of flutes is pref-- erably providedon. roughing hobs; containing l front rake and side rake." When the-r'oughinghob tothe handof flutes 31 in Fig.16, and when the e of the type indicated in Fig ;lc is single threaded, '1, A Ipreferablyprovidehelical flutes of a handequal= roughing hob is multiple threaded; I may provide a either helical flutes'lor straight 'flutes extending parallel to the hob axisg QThefprofilelof enuc is; 1 madepreferably as indicated in'Fig;4 at38. FiK-i,

9sh0ws a roughing hob in development; Its ,flutes" '70 arethelica l and. areseen to have the sam'ehand-vi asthei hand oifthe hobthread, 71f

While-I have described-c roughingliobs. my, V with reference to the embodiment oi Fig. '1' it;- is f understood 'that the;described"principlesymaygbe generally applied and that flutesof I such, char-. acter'arerprovidediwhich fayor the-cutting edge'sj; doing most of the "cutting work. Theflutes L of; roughing Ihobs arethen generally diiferentffrom the 'flutesof finishing hobs..f;= When-the tooth. number of the is: small, it isgfound difficult.to-completelysepiz 1 2. arate thecutting teeth for-finishing the .two 1, sidescrespectiyely oi the teethoflthe gear blanks, hob- 72 embodying a rack of increased pressure angle 'is' then" preferablyproyided, .see Fig; 10.1 The said'rack r'nesheslwith the gear blankalong"; I I 1ines 73',- '74 in suchfmanner that alin'e -[7,5,ofthe i rack rolls onia circle'76. Of'the'gear blankri Circle 1. 76 is seen tov be outside "of; the pitch circleflfln Thehob '72 ispreferably]provided"with"straights flutes 78 (Fig, 11) extendinglinthefldirectionlof the "hob axis andlcontai'ning'a-front rakey The cutting faces of the hob fare thereforenot:radial r but hooked or. undercut. iAf-r front rake favors; the two sides 79, 80 of: the cutting; teeth "equally; [as is known, and the more;"the' larger- Tthe innw clination 'of'saidisides, that isto say "the larger gear bank,

the pressureangle of: the :hob. The combination "The Figuresi 12 and 13 are to "indicate; that of Ia hob 'lhaying anincreased" pressureangle and frontrake, in .accordance'with the lpresent inf vention; is' therefore particularly advantageous =1: for cuttingqgears having small numbersfof-jteetha Ifers fromthe conventional nethods of hobbing,

through the-shape of the hob and-frequently also through the. angulansetting of the hob-.1 In a a preferred embodiment gofg'the invention; a-hob 5 ,--gejar"-blankis to mesh, with a mate g'ean- 'In ad-J- and blank correspond to known pra'ct ice.

embodies andrepresents through its shape-and itspositi'on a rack of differentjpressureangleasv compared: withl the pressure angle at which the ditionac-hobcontains cutting faces with a rake, so astoeffect cutting angles smaller than; 90

- I on: the "cutting.edgesfor'finishing either sideof the teeth of thegear blank. Themotions of tool? Hob and blankarerotated in timed relation on their r, respective axes-while .a feeding, motion isiprothe relative position oftool. and blank in plan vided betweenhob and blank, ordinarily in the hob axis 97: and offset from said axis. an aniOunt proportional to the difference between thesetting direction of the axis of theblank."

Anelevational ;view of a simplified devicefor hobbing gears in accordance with. thez'presentinvention is shown 'in'Fig'. 15, while Fig: 14 shows shownin' engagementwitha gear blank 84. Thez hob 83Qcontains a rake so as to efiect cutting anglesv smaller than 90 on the finish cutting" edges for. finishing'one. sideof the teeth of a gear blank as well as on the finishxcutting edges. for finishing the other Through its shape and its position hob 83 embed-:-

side of saidzteeth; 1

ies or represents-a rack: having a "pressure angle other than the pressure angle of the gear blank:

84. :Hob-83is rotatedon its axis 85 by'a'pplying motion to'a gear. 86 in any suitable known 'manner. Gear blanks is turned on itsaxis intimed ,relation to thehobiby means'of a gear 87,which are displaced relatively to each other in the di- 'cal and herringbone gears will 'now' be'described receives motion from a pinion 88. --The latter-is operativelyconnected with thehob 83 through shaft 89" and hypoid gears 90. "During the cut-a1 tingoperation, the slide 91 on which the hob is in the direction of the axis of the An application of the present invention to hellwith reference to the Figures 16' to 20. When. exactlythe same principles are applied tothe production of'helical teeth as have beendescribed particularly forstraight teeth it .is usually found that the two sides of .the teeth are finished along lines 22, 23, (see Fig. 1'7 and Fig. 18) which rection of the axis 'of the'gear blank lol. In oth'erwords one side of the teeth'is finishedsomewhatahead of "the other. 'While' this feature does notconvey any inaccuracyv or error, it is [considered a drawback, because it necessitates an increased'dis'ta nce of feed, and in-the case of herringbone gears it also necessitates an increase .of the gear teeth along lines of substantially equal position relatively to the axis of the gear blank, that "is to, say relatively to the direction of I clearance bet-weenfthehelical teeth of opposite hand, as isreadily understood.

It is: generally desirable'to finish the two. sides feed. Referring to Fig. 16, it isdesirable to finish the two sides of the gear teeth along'lines 22',

23'," whose end points lie substantially in the same planes92, 9 3 perpendicular to the gear axis.

"Io this end a new feature is added;as will now be describedz I r I We will consider a plane section'through thehob thread, along .lines 7 Ski- 94 of Fig. 18, the

sectional plane being offset from the-hob. ,axis:.a,c

Qthan tIle meanlead angle-of the hob thread, de-.

'. of the gear-blank. The-shape of the hob thread distanceiequal; to themean radiusof the hob.

thread., Reference is made to 1 Fig. 20, which shows the hobthread in engagement with an im-' I rackteethshown in Fig. '18. a

pass through points 98v of projected axis 937,- the 7 location. of which points 98 can be determined from Fig.;1,8.- U

' When, however :the'hob set to an angle different from said lead angle, and in the present instance larger;than said lead angle, then thehob thread may be made-to contact with the shown rack section inxpoints: of lines 100, see;

Fig. '19. Lines 100 are parallel to the projected;

angle of the hob and its mean leadangle. The

setting angle is herein understood to. be the angle; I

between the hob axis and the projected normals of the rack teeth. 'The'points 98=are then located,

on the; lines 100 (Fig. 19) andtheir'location is.

seen to effect adesirable equal axial position of, the two lines 22323. 1 a j In the case ,of'helicaliteeth or double helical or herringbone teeth, the hob. is thereforepref-l; erablyset to an agle other thanitslead angle insuch a way as to effect, finishing 1lines 22,-23' 1 of aboutequal position axially ot the gear blank.

:A mathematical'analysis revealsv that for pro- I ducingfinvolute gears, the thread surfaceof hob set-:in accordance withFig. 19, is' still 311,11)

volute helicoidal surface, containing. involutes -in Moreover thehperpendicul'ar pitch or normal sections at right anglesto the faxisof thethread,

in Fig. 1), remains the same and is independent,

.of the: settingof .the hob. .The perpendicular; pitch of any-hob should always be .equal toithe I perpendicular pitch ofthe involute gear-teeth.

A -general method will now briefly bedescribedl threads. wThis method is applica ble for any 'sys-i First the rack; is'determined on which the genby applying the considerations. -pre viously set,

for determining the characteristics; of .ghob; V

forth, which call forarack of reduced pressure;

angle,when the tooth number of the gea r blanlcf is large; and whichcall for, a rack; of increased. pressure angle when thetooth numberflof the]; gear. blank is small. I An angular setting is then tentativelyassumed for the hob axis, the setting' angle corresponding to an angle larger or smaller.

pending on whether the. pressure. angle of the embodied rack has been; reduced or increased respectively, as compared with the pressure angle is then-experimentally determined 'as the thread conjugate to'a known rack." This known prob lem can i be solved inknown; mannerby cov ering" the surface of said rack'with a moving cutting a tool, while providing such motion between tool and hob, thread as corresponds to thernesh be-, tween saidrack and said-,hob thread. The hob thread is then brought into mesh with'a gear equal to a finished gear; blank, andthelines described on the toothvsurface of said gear by moving points of contact arethen experimentally tion, the shape of the hob and itsposition being a )dete iiu e i s ance k vwm manner by .c' y neijih sn his t e t h e ed. and J watching the spots rubbed off through the tooth The a feature: of i setting the hob,

other than its lead angle, relatively to a direction .inventiomii-so desired.

na ns, ma h m d m nin ht m as f l ,withint escopeof the,appendedelaimsl ,1 t I .rwhatlr e m 5:5,; t t:

' 1. The method of generating-gears, whichcon sists inflprovidingahob having two groups 01 l 'fit fid es suited to; finish the two sides resp'ecgtivelypf the teeth ,ofga'gearrblank, said cutting jedges being inclined j-to planes, perpendicular to i {the hob axis at angleslarger than four degrees ;(4 all the finish cutting vedges 'of one group beingv disposedoniother cutting teeth than the I finish cutting edges of the other group of" the hob, in'prqviding fiutes'of difierentinclination on the two groups to form keen cutting edges, in p0si-'-- tioning the hob in engagement with a gear blank, in rotating hob? and blank in timedrelation, the

i a surface other than the pitch surface offthe gear blank; and in providing feeding motion between hob andblank in the direction of the axis-of the 2. The method of generating gears, which consists in providing a hob having two groupsj of cutting edgessuited to finish the two sides respectively of the teeth of a gear blank, said cutting the hob axis at angles larger than four degrees .(4 in providing flutes'of different inclination on said two'groups-to formlkeen cutting ledges,

in. positioning the hob in engagement with :a gear blank, in rotating hob and blank in timed relasuch thatsaid hob represents a toothed'member meshing with the gear blank while said member rolls ona cylindrical surface concentric with the gear blank, and in providing feeding motion be,- tween hob and bla kin the direction of the axis oftheblank. J r fl '3'. The method of generating gears, which con- :sists in providing two groups of cutting edges suited'to finish the two sides respectively of the gear blank, saidcutting edges being incline d to planes perpendicular to the hob' axis at angles larger than four degrees (4) innproviding heli: I cal flutes of opposite hand on said two groups to iormkeen cutting edges, in rotating said' cutting edges on a common axis in engagement with a gear blank," in rotating said gear blank, the shape andthe'jposition of said cutting edges being such that said cutting edges represent a rack meshing with the gear blank, and in providingfeeding motion between cutting edges and blank in the direction of the axis of the blank. 1

ormal;- to t he, teethpf the embodied rack, may be used. independently of theotherfeature s' ,oi thegagement with each other, an in pr ,ing motion between ihob; and blank.

shape of the hob and its position being such that said hob represents a toothed member rolling'on' H pressure angle of saidthreadbeinglarger than edges being inclined to planes perpendicularto.

rgear blank in engagement with each other, and

than 'one half of said pressure angle, so that of the gear lto beicut and being, 1arger"than one .eds ibein i e t Plene p rpend u a to a h 9? ax s t an es larger thenti u ideer e such that said hob represents 'a rack; meshing iwith,thegearll blank, andi in providing jre qiiig ss ,jf .;n otion betweenhob' and'blankr; a 5. The1 m et hod of cutting gears rto stsm- I profile, which consists :in providin a hobf havin g twofgroups offcutting edges suitedto' finish the e v. a 1 two sides;respectively' of the teeth of aIge'larQQO biank, said cutting edges beinginclined Qto pla'nes perpendicular lto thehob axisat; angles larger.

th n P d E i IK D 'i kpm i ii h li el ufi of opposite hand on said two groups to form keen f cutting edges; ;in]rotating hob and blank in. en- 1 i r b' idine f e 1 he method of cutting gea which sists-'nfprovidin two-groups oficuttingedges: suited to: finish the itwo sides respectively. of, the g teeth of a, gear blank, 'said cutting ed es being inclineditolplanes perpendicularto, the' hob axis i atangles jlarger thando game es-(4), npreviding flutesfof diiferent inclination on "said two groups, the profile'g of thegnutesiof atfleast one11G5 of the groups beinghoriradial in a plane .at right I ,7 i angles to th axis ofirotat n in rotatin jsaidfl r I I cutting edges on a comrnon ax'i'fs' in engagement Y with a gear blank,in rearing said blank, and in providing feeding, motion between" said cutting .110,

edges and said gear blanki' 7. The method of generating gears, which consists in providinga gear: blankdand a hob having cutting teeth disposed in a; thread, the

tion-onthe cutting teeth"for"finishing said two sides respectivelmin rotating "said'hob and said in providing feeding motion between said hob and said gear blank in the direction of. the axis of the'gear blank. 1 i 8. The method of generatingfgears, which the pressure angle oil-said threadbeing smaller than the pressure'angle of said gear and larger the cutting teeth for finishing the two sides of the gear teeth have diiferent positions with'ref spect to thehob axis, in providing cutting faces; of different inclinations on saidicutting'teeth, in" .1 a

rotating said hob and said gear blank in engagement with each other, and ingproviding feeding motion between said hobtvand said gear "14d 'blank in' the direction of -the axis of the gear blank." e 9. ;'I.h e,met ho'd of generating gearsgwhich conl sists in providing a gear, blank and two separate 1, I

half of said pressure-angle, efiecti'ng acute it'he ,two sides of saidthread being formed to -mesh with the desired gear along two lines of action askewto'one another and whose pressure.

' angles difier from the pressure angle of said cutting angles on said clitting fedges by "pro- 'viding flutes of opposite hands 'on said two groups, in rotating. said cutting edges on a common axis in -engagement with said gear blank,-

'inturning'said blank on its axis in timed rela tlQIlftOthfl rotation of said cutting'edgeslan d in effecting feeding motion between said cut ting edges-and said gear blank lengthwise of the axis of said gear blank; I

10. The method or generating gears, which consists in providing agear blank and. a hb having cutting edges disposed in a helical thread,

"gear, in rotatingisaidfhob and said gear blank on-their respective axes in timed relation'to each other, and iri effecting feeding motion between 'said'hob and said'gear blankin thedirectionof the axis of th e gear blank, I r

11. The method of generating gears, which consists in providing a gear blank and ahob havj ing, cutting edges disposedin a helical thread,

thetwo sidesfiof said'threadi-being formed to gmesn with the desired'ge'ar along twolines of 3 action askew' to one another and whose pres sure angles are ismallerfthan the pressure angle of said gear, in rotating said hob and said-gear blank ontheir respective axes in timed relation to :eachother', and; in' effecting, feeding motion "between said'hob'an d'said gear blank in the direction'of the axi'sof' the'gear blank;

V of saidthre'adibeing' ro'r'medfl'to mesh; with we desiredgear along two'line's'of, actionaskew: toeaifch with respect to each other, in. rotatingu said hob blankin blank." r a g j 1 The method of generating-helical gears, herringbone gears and worms; which "c'onsists ini to each other and whose pressure "angles are speet 't0;--each' other, in rotating said hob and said gear'blank on their "respective axes intimed the 'dire'otion of the axis of'the gear blank. 7

other, said'line's of action being displacedcsub- I stantially in the'direction'of the "gearperiphery and said; gear blank 'on'their respective axes in timed relation toeach' other, and inf-effecting feedingrnotion between said hob and said-gear the direction of the axis 'of'the gear v roviding a gear blank and a hob having' cut- "ting iedges' disposed in a helical thread, the two sides of said "thread being formed to mesh with the desired gear along two lines'of actionaskeW smaller than I the pressure angle-for said gear, said lines of 'action bieing. displacedsnbstantially in the :direction of theggear pe'riphery'with re- 7 relation' 'to-each other-,-and in effecting feeding' motionbetween said hob and said gear bla'nk in :EaNEsT; VWILLDHABYER. 

